Establishing Product Concentration Benchmarks for Two Step Tandem Electrochemical Conversion of CO2 to C2H4

Despite the strong focus on developing electrochemical conversion systems for upgrading CO2 to C2+ hydrocarbons, the downstream separations required to complement the reactors have received relatively less attention. In this work, we develop materials for the separation of two critical binary gas mixtures, CO2/CO and C2H4/CO. These mixtures are produced in a tandem reaction system that first upgrades CO2 to CO in a solid oxide fuel cell, followed by reduction of CO in a separate electrolyzer that produces ethylene. We then model the entire plant, including gas and liquid separation systems to determine the effect that product concentrations from the reactor have on the overall process economics. Our analysis shows that effective gas separations via pressure swing adsorption processes, using the materials developed in this work, significantly enhance the Net Present Value of the plant, rendering gas separation no longer a limiting factor in process economics. However, liquid product concentrations at ~1 wt% (typical of current literature) and high CO2 capture costs (> $50/ton) can make the process economically unviable.